1. Field of the Invention
The present invention relates to a CATV system and a communication method therefor, and more particularly to a technique to connect to the internet from a terminal via a CATV net.
2. Description of the Prior Art
When a user in a household connects to the, internet by a computer such as a personal computer, generally he or she individually makes a contract with a provider of the internet connection service and connects to the internet via the public telephone line with the aid of the provider""s service. Contrary to this, there has recently been examined a method of connecting the internet via an existing CATV net.
However, the existing CATV net is originally designed to supply video and/or audio data from the center to the subscribers, and its upstream transmission band is extremely narrower than the downstream transmission band. Concretely, in a general CATV system, the upstream transmission lines are assigned to the frequency band of 5-50 MHz, and the downstream transmission lines are assigned to the frequency band of 50-450 MHz. The downstream transmission band is relatively broad in order to transmit multi-channel television signal to the terminals of the subscribers as the original role of the CATV system. In contrast, the upstream transmission lines are used only for the transmission of control data such as accounting data to the subscribers, and hence its bandwidth is originally very narrow. Therefore, it is difficult to use the existing CATV net for the internet connection, i.e., bidirectional communication.
It is an object of the present invention to provide a CATV communication system and a communication method which enable the internet connection via the existing CATV net.
According to one aspect of the present invention, there is provided a CATV communication system including a center and a plurality of terminal devices connected via a CATV net, the center including: a first transmitter for transmitting, to the terminal device, upstream channel use information representing unoccupied channel out of a plurality of upstream channels; a first detector for detecting channel get request from data transmitted from the terminal device; a second detector for detecting a presence of the unoccupied channel in the upstream channels when the channel get request is detected; a second transmitter for assigning one of the detected unoccupied channels to the terminal device which has transmitted the channel get request and for transmitting channel assign data including a designation of the assigned channel to the terminal device when the unoccupied channel is detected; and a first communication unit for performing data communication with the terminal device via the assigned channel, and the terminal device including: a second communication unit connected to a computer for performing communication with the computer; a third detector for detecting center-directed data, to be transmitted to the center, which is included in the data received from the computer; a fourth detector for detecting the upstream channel use information from the data transmitted from the center when the center-directed data is detected; a third transmitter for selecting one of the unoccupied channels on the basis of the upstream channel use information and for transmitting the channel get request designating the selected channel to the center; a fifth detector for detecting the channel assign information from the data transmitted from the center; and a third communication unit for performing data communication with the center by using the upstream channel designated by the channel assign information for data transmission after the channel assign information is detected.
According to another aspect of the present invention, there is provided a center connected to a plurality of terminal devices via a CATV net, including: a first transmitter for transmitting, to the terminal device, upstream channel use information representing unoccupied channel out of a plurality of upstream channels; a first detector for detecting channel get request, including a designation of a channel to be used, from data transmitted from the terminal device; a second detector for detecting a presence of the unoccupied channel in the upstream channels when the channel get request is detected; a second transmitter for assigning one of the detected unoccupied channels to the terminal device which has transmitted the channel get request and for transmitting channel assign data including a designation of the assigned channel to the terminal device when the unoccupied channel is detected; and a first communication unit for performing data communication with the terminal device by using the assigned channel for data transmission.
According to still another aspect of the present invention, there is provided a terminal device connected to a center via a CATV net, including: a first communication unit connected to a computer for performing communication with the computer; a first detector for detecting center-directed data, to be transmitted to the center, which is included in the data received from the computer; a second detector for detecting upstream channel use information representing an unoccupied channel out of a plurality of upstream channels from the data transmitted from the center when the center-directed data is detected; a first transmitter for selecting one of the unoccupied channels on the basis of the upstream channel use information and for transmitting the channel get request designating the selected channel to the center; a third detector for detecting channel assign information from the data transmitted from the center, the channel assign information being transmitted by the center in response to the channel get request and assigning an unoccupied channels; and a second communication unit for performing data communication with the center by using the upstream channel designated by the channel assign information for data transmission after the channel assign information is detected.
In accordance with the CATV system thus configured, the center transmits the upstream channel use information representing the unoccupied channel to the terminal device. When there is data to be transmitted to the center, the terminal device detects the upstream channel use information from data transmitted from the center, selects one of the unoccupied upstream channel, and transmits the channel get request to the center. On receiving the channel get request, the center checks the channel occupancy condition at that time to examine whether or not the channel designated by the channel get request is occupied. If it is unoccupied, the center determines to assign the channel to the terminal device which has transmitted the channel get request, and transmits the channel assign information to the sender terminal device. When receiving this channel assign information, the terminal device judges that the use of the channel is permitted, and performs data communication with the center by using the channel for data transmission. Therefore, by transmitting the channel use information and the channel get request between the center and the terminal device, the internet connection via the CATV communication system may be achieved with making the best use of the channels of limited number.
The center may be configured to receive the channel open request and to forcibly disconnect the channel designated: by the channel open request. By this, vain channel use may be avoided and the usage efficiency of the communication line may be improved. In addition, if the system is configured such that the center sends the channel open confirmation information to the terminal device before actually disconnecting the channel, erroneous disconnection due to noise or the like may be avoided. Further, the center may be configured to forcibly disconnect the channel if the communication condition of the channel is not normal. By this, the communication can be appropriately terminated in the system failure or accident.
If the center is configured to have a control LAN for control operation and a center LAN, independent of the center LAN, for data communication, the control operation may be separated from the data communication, thereby reducing the possibility of system error or confusion. If the terminal device is configured to transmit the channel use information to the center and the center forcibly disconnect the non-used channel, the line usage efficiency may be improved
The terminal device may configured to select the channel for the channel get request by using the random number. In addition, the terminal device may transmit the channel get request by a signal having the power determined by the random number and/or transmit the channel get request at the timings determined by the random number. With these modifications, the unevenness or deviation in the selection of the channel is avoided, and the possibility of collision of the channel get requests sent from plural terminal devices may be effectively avoided. The center and the terminal device may perform the data communication by using the cable packets which include control data and internet protocol. Therefore, both IP frame and control data can be transmitted by the cable packets, and the protocol can be simplified.
According to still another aspect of the present invention, there is provided a CATV communication method for performing a communication between a center and a plurality of terminal devices connected via a CATV net, the method including the steps of: transmitting, from the center to the terminal device, upstream channel use information representing unoccupied channel out of a plurality of upstream channels at every predetermined time period; detecting, in the terminal device, center-directed data, to be transmitted to the center, which is included in the data received from a computer to which the terminal device is connected; detecting, in the terminal device, the upstream channel use information from the data transmitted from the center when the center-directed data is detected; selecting, in the terminal device, one unoccupied channel on the basis of the upstream channel use information and transmitting the channel get request designating the selected channel to the center; detecting, in the center, channel get request from data transmitted from the terminal device; detecting, in the center, a presence of the unoccupied channel in the upstream channels when the channel get request is detected; assigning, in the center, one of the detected unoccupied channels to the terminal device which has transmitted the channel get request and transmitting channel assign data including a designation of the assigned channel from the center to the terminal device when the unoccupied channel is detected; detecting, in the terminal device, the channel assign information from the data transmitted from the center; and performing data communication between the center and the terminal device by using the upstream channel designated by the channel assign information for data transmission after the channel assign information is detected.
According to still another aspect of the present invention, there is provided a CATV communication method for performing a communication between a center and a plurality of terminal devices connected via a CATV net, the method including the steps of: transmitting upstream channel use information representing unoccupied channel out of upstream channels from the center to the plurality of terminal devices; detecting the upstream channel use information if there is data to be transmitted to the center, selecting one of the unoccupied channels and transmitting channel get request to the center if the upstream channel use information is detected; checking a condition of occupancy of the requested upstream channel when receiving the channel get request in the center, assigning the channel to the terminal device which has transmitted the channel get request if the requested channel is unoccupied, and transmitting channel assign data including a designation of the assigned channel to the terminal device; and transmitting the data to the center via the assigned upstream channel when the terminal device which has transmitted the channel get request detects the channel assign information.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.